This invention relates to additives for improving the processability of vinyl chloride polymer compositions. This invention further relates to lubricants which stabilize the rheological properties, particularly the melt viscosity, of molten vinyl chloride polymers.
Paraffin and polyethylene waxes are conventionally employed as lubricants for rigid vinyl chloride polymer compositions. It is well known to use these lubricants in combination with salts of stearic acid or other fatty acids containing from 8 to about 20 carbon atoms to control rheological properties and impart stability during processing of rigid vinyl chloride polymers. In the absence of a stabilizer vinyl chloride polymers degrade readily at the high temperatures required to process these materials. This degradation may appear as an increase in melt viscosity, which may or may not be accompanied by discoloration. It is believed that the discoloration results from a conjugated series of double bonds between adjacent carbon atoms of the polymer chains. Metal salts of fatty acids may be less than desirable additives when the polymer remains molten for extended periods of time, since they often contribute to an increase in melt viscosity during the initial stages of polymer degradation. Any disruption of laminar flow in the processing equipment could cause a portion of the polymer stream to degrade slightly, resulting in a melt viscosity increase within that portion of the polymer. The lower viscosity material on the upstream side of the slower moving, more viscous portion would eventually force its way around and through the slower moving portion and appear as light colored spots or streaks in the final shaped product.
It is an objective of this invention to define improved lubricant systems which not only facilitate processing of vinyl chloride polymers but, in addition, function as melt viscosity and color stabilizers for these polymers and are compatible with conventional heat stabilizers, including organotin compounds and alkaline earth metal salts of fatty acids.